Method for performing HARQ for relay station

ABSTRACT

A method for performing HARQ includes: receiving information to determine downlink subframes used for a relay station to receive scheduling information from a BS; determining uplink subframes for performing a HARQ with the DL subframes, each of the UL subframes corresponding to each of the DL subframes; assigning sequentially each of a plurality of HARQ processes to each of the UL subframes one by one; and performing HARQ with the BS at at least one of the HARQ processes. An n-th subframe is configured for a corresponding UL subframe if an (n−4)-th subframe is configured for one of the DL subframes, n denoting an integer. The HARQ processes are equal in number to the UL subframes. The DL subframes are configured in at least one radio frame having 10 subframes indexed from 0 to 9. Subframes having indexes 0, 4, 5 and 9 are not configured as a DL subframe.

CROSS-REFERENCE TO RELATED APPLICATIONS

This application is a continuation of U.S. patent application Ser. No.13/941,803, filed on Jul. 15, 2013, now U.S. Pat. No. 8,982,771, whichis a continuation of U.S. patent application Ser. No. 12/920,584, filedon Sep. 1, 2010, now U.S. Pat. No. 8,514,766, which is the NationalStage filing under 35 U.S.C. 371 of International Application No.PCT/KR2009/006961, filed on Nov. 25, 2009, which claims the benefit ofearlier filing date and right of priority to Korean Patent ApplicationNo. 10-2009-0022797, filed on Mar. 17, 2009, and also claims the benefitof U.S. Provisional Application No. 61/119,380, filed on Dec. 3, 2008,the contents of which are all hereby incorporated by reference herein intheir entirety.

TECHNICAL FIELD

The present invention relates to wireless communication and, moreparticularly, to a method for performing HARQ for a relay station.

BACKGROUND ART

An error compensation technique for ensuring reliability ofcommunication includes a forward error correction (FEC) scheme and anautomatic repeat request (ARQ) scheme. In the FEC scheme, an error at areception end is corrected by adding an extra error correction code toinformation bits. In the ARQ scheme, an error is corrected through dataretransmission, for which there are a stop and wait (SAW) scheme, ago-back-N (GBN) scheme, a selective repeat (SR) scheme, and the like.The SAW scheme is a scheme in which whether or not a transmitted framehas been properly received is checked and then a next frame istransmitted. The GBN scheme is a scheme in which N number of successiveframes are transmitted, and if a successful transmission is not made,every transmitted frame subsequent to an error-generated frame isretransmitted. The SR scheme is a scheme in which only anerror-generated frame is selectively re-transmitted.

The FEC scheme is advantageous in that a time delay is small and thereis no need to transmit and receive information between a transmissionend and a reception end, but a system efficiency is degraded in a goodchannel environment. The ARQ scheme has a high transmission reliabilitybut is disadvantageous in that a time delay occurs and a systemefficiency is degraded in a poor channel environment. A hybrid automaticrepeat request (HARQ) scheme combining the FEC and ARQ has been proposedto resolve such shortcomings. According to the HARQ scheme, whether ornot data received by a physical layer has an error that cannot bedecoded is checked, and if the data has an error, retransmission of datais requested to thus enhance performance.

The receiver of the HARQ scheme basically attempts an error correctionon received data and determines whether or not data retransmission isrequired by using an error detection code. As the error detection code,a cyclic redundancy check (CRC) may be used. When an error of receptiondata is detected through the CRC detection process, the receivertransmits the NACK signal to the transmitter. Upon receiving the NACKsignal, the transmitter transmits proper retransmission data accordingto the HARQ mode. Upon receiving the retransmission data, the receivercombines the previous data and the retransmission data and decodes thesame to thereby improve reception performance.

The retransmission scheme of the HARQ may be classified into asynchronous scheme and an asynchronous scheme. In the synchronous HARQ,data is retransmitted at a point of time both the transmitter and thereceiver knows about, so signaling required for transmission of datasuch as an HARQ processor number or the like can be reduced. In theasynchronous HARQ, resources are allocated at an arbitrary time forretransmission. The asynchronous HARQ provides flexibility of resourceallocation.

Meanwhile, the wireless communication system may include a relay station(RS) in addition to a base station (BS) and a mobile terminal (MS). TheRS serves to extend a cell coverage and improve a transmissionperformance. When the BS provides a service to an MS located outside thecoverage of the BS via the RS, the RS may relay both control signals anddata signal between the corresponding MS and the BS, thus extending thecell coverage of the BS. In addition, when the BS provides a service toan MS located within the coverage of the BS via the RS, the RS mayamplify a data signal between the BS and the MS and transfer theamplified signal to each reception end, to thereby improve atransmission performance. The presence of RS is required especially whenan MS is in a shadow area within the coverage of the BS.

When the RS is disposed between the BS and the MS, performing HARQ isproblematic. The reason is because HARQ generally considers only aone-to-one situation between the BS and the MS, so the presence of RSrequires consideration of HARQ between the RS and the BS and HARQbetween the RS and the MS. In particular, if the synchronous HARQ isperformed between the BS and the MS in the conventional wirelesscommunication system, how to perform HARQ of the RS without affectingthe synchronous HARQ matters.

DISCLOSURE OF INVENTION Technical Problem

An object of the present invention is to provide a method for performingHARQ for a relay station.

Another object of the present invention is to provide a relay stationthat performs HARQ.

Solution to Problem

In an aspect, a method for performing a hybrid automatic repeat request(HARQ) by a relay station (RS) in a wireless communication system isprovided. The method includes performing HARQ with a mobile station(MS)by a fixed HARQ period, and performing HARQ with a base station(BS) by aHARQ period series, wherein the HARQ period series comprises a pluralityof HARQ period series element (x_(k), y_(k)), where (x_(k), y_(k))indicates that when data is transmitted in n-th subframe, an ACK/NACKsignal is received in (n+x_(k))-th subframe and the data isretransmitted in (n+x_(k)+y_(k))-th subframe when the ACK/NACK signal isa NACK signal, wherein at least one of x_(k) and y_(k) for one HARQperiod in the HARQ period series is different from at least one of x_(k)and y_(k) for the other HARQ period in the HARQ period series.

The sum of x_(k) and y_(k) for each HARQ period in the HARQ periodseries may be same.

The sum of x_(k) and y_(k) for each HARQ period in the HARQ periodseries may be eight.

The HARQ period series may comprise HARQ period series elements (6, 2),(4, 4), (5, 3), (4, 4) and (4, 4).

The HARQ period series may comprise HARQ period series elements (4, 4),(4, 4), (5, 3), (4, 4) and (4, 4).

The fixed HARQ period may be equal to an HARQ period in which the RSperforms HARQ with a mobile station (MS).

The fixed HARQ period may be an interval of 8 subframes.

The HARQ periods in the HARQ period series may cyclically be shifted.

In another aspect, a relay station (RS) includes a transceiverconfigured to transmit or receive a radio signal, and a processorconnected with the transceiver and performing hybrid automatic repeatrequest (HARQ), wherein the processor performs HARQ with a MS by a fixedHARQ period and performs HARQ with a BS by a HARQ period series, whereinthe HARQ period series comprises a plurality of HARQ period serieselement (x_(k), y_(k)), where (x_(k), y_(k)) indicates that when data istransmitted in n-th subframe, an ACK/NACK signal is received in(n+x_(k))-th subframe and the data is retransmitted in(n+x_(k)+y_(k))-th subframe when the ACK/NACK signal is a NACK signal,wherein at least one of x_(k) and y_(k) for one HARQ period in the HARQperiod series is different from at least one of x_(k) and y_(k) for theother HARQ period in the HARQ period series.

Advantageous Effects of Invention

The method for performing HARQ between a relay station and a basestation or between a relay station and a mobile terminal is provided.Even if a blank frame is generated from the relay station, collision canbe avoided. The relay station can perform HARQ while maintainingcompatibility with an existing synchronous HARQ.

BRIEF DESCRIPTION OF DRAWINGS

FIG. 1 illustrates a wireless communication system.

FIG. 2 illustrates a wireless communication system including relaystations.

FIG. 3 illustrates a radio frame structure in a 3GPP (3^(rd) GenerationPartnership Project) LTE (Long Term Evolution).

FIG. 4 illustrates an example of a synchronous ACK/NACK transmissionscheme.

FIG. 5 illustrates performing of synchronous HARQ between a relaystation and a base station when there is a non-blankable subframe.

FIG. 6 is a flow chart illustrating the process of an HARQ performingmethod according to an exemplary embodiment of the present invention.

FIG. 7 illustrates performing of HARQ by the 8 sub-frame periods on arelay station-base station link when non-blankable subframes are #0, #4,#5, and #9 according to an exemplary embodiment of the presentinvention.

FIG. 8 illustrates the types of HARQ processes defined in FIG. 7.

FIG. 9 illustrates the types of HARQ processes defined in FIG. 7.

FIG. 10 illustrates performing of HARQ by the 8 sub-frame periods on therelay station-base station link when non-blankable subframes are #0 and#5 according to an exemplary embodiment of the present invention.

FIG. 11 illustrates the types of HARQ processes defined in FIG. 10.

FIG. 12 illustrates the types of HARQ processes defined in FIG. 10.

FIG. 13 illustrates an example of using two HARQ processes in whichreception band subframes from a base station are not overlapped.

FIG. 14 illustrates an example of sequentially setting and using twoHARQ processes with reception band subframes from a base station whichare not overlapped.

FIG. 15 illustrates an example of using two HARQ processes by permittingoverlap of reception band subframes from a base station.

FIG. 16 is a schematic block diagram of a relay station according to anexemplary embodiment of the present invention.

MODE FOR THE INVENTION

The following technique may be used for various wireless communicationsystems such as a code division multiple access (CDMA), a frequencydivision multiple access (FDMA), a time division multiple access (TDMA),an orthogonal frequency division multiple access (OFDMA), a singlecarrier-frequency division multiple access (SC-FDMA), and the like. TheCDMA may be implemented by a radio technology such as universalterrestrial radio access (UTRA) or CDMA2000. The TDMA may be implementedby a radio technology such as a global system for mobile communications(GSM)/general packet radio service (GPRS)/enhanced data rates for GSMevolution (EDGE). The OFDMA may be implemented by radio technology suchas IEEE (Institute of Electrical and Electronics Engineers) 802.11(Wi-Fi), IEEE 802.16 (WiMAX), IEEE 802.20, E-UTRA (Evolved UTRA), andthe like. The UTRA is a part of a universal mobile telecommunicationssystem (UMTS). 3GPP (3^(rd) Generation, Partnership Project) LTE (LongTerm Evolution) is a part of an evolved UMTS (E-UMTS) using the E-UTRA,which adopts the OFDMA in downlink and the SC-FDMA in uplink.

For clarification, the following description will be centered on 3GPPLTE, but the technical idea of the present invention is not meant to belimited thereto.

FIG. 1 illustrates a wireless communication system.

With reference to FIG. 1, the wireless communication system 10 includesat least one base station (BS) 11. Each BS 11 provides a communicationservice to particular geo-graphical areas (which are generally calledcells) 15 a, 15 b, and 15 c. Each cell may be divided into a pluralityof areas (which are called sectors). One or more cells may exist in asingle BS.

A mobile station (MS) 12 may be fixed or mobile, and may be referred toby other names such as user equipment (UE), user terminal (UT),subscriber station (SS), wireless device, personal digital assistant(PDA), wireless modem, handheld device, access terminal (AT), etc. TheBS 11 generally refers to a fixed station that communicates with the MS12 and may be called by other names such as evolved-node B (eNB), basetransceiver system (BTS), access point (AP), an access network (AN),etc.

Hereinbelow, downlink (DL) refers to communication from the BS 11 to theMS 12, and uplink (UL) refers to communication from the MS 12 to the BS11. In the downlink, a transmitter may be a part of the BS 11 and areceiver may be a part of the MS 12. In the uplink, a transmitter may bea part of the MS 12 and a receiver may be a part of the BS 11.

FIG. 2 illustrates a wireless communication system using a relay station(RS). In uplink transmission, a source station may be the MS and adestination station may be the BS. In downlink transmission, a sourcestation may be the BS and a destination station may be the MS. The RSmay be the MS, or an extra independent RS may be disposed. The BS mayperform functions such as connectivity between the RS and the MS,management, controlling, and resource allocation.

With reference to FIG. 2, a destination station 20 communicates with asource station 30 via a relay station 25. The source station 30 sendsuplink data to the destination station 20 and to the relay station 25,and the relay station 25 re-transmits the received data. The destinationstation 20 also communicates with the source station 31 via relaystations 26 and 27. In uplink transmission, the source station 31 sendsuplink data to the destination station 20 and the relay stations 26 and27, and the relay stations 26 and 27 retransmits the received datasimultaneously or sequentially.

There are shown the single destination station 20, three relay stations25, 26, and 27, and two source stations 30 and 31, but the presentinvention is not limited thereto. Namely, the number of destinationstations, relay stations, and source stations included in the wirelesscommunication system is not limited.

As a relay method used in the relay stations, any methods can be such asan amplify and forward (AM), a decode and forward (DF), or the like, andthe technical idea of the present invention is not limited thereto.

The wireless communication system supports a hybrid automatic repeatrequest (HARQ). In downlink HARQ, the BS transmits downlink data to theMS, and the MS transmits an ACK/NACK(Acknowledgement/Negative-Acknowledgement) signal regarding whether ornot the downlink data has been successfully received. When the downlinkdata is successfully decoded, the ACK/NACK signal is an ACK signal,whereas if decoding of the downlink data fails, the ACK/NACK signal is aNACK signal. In uplink HARQ, the MS transmits uplink data to the BS, andthe BS transmits an ACK/NACK signal regarding whether or not the uplinkdata has been successfully received. HARQ can be divided into asynchronous HARQ and an asynchronous HARQ. The synchronous HARQ is ascheme in which data is transmitted at a point of time the BS and the MSknows about. The asynchronous HARQ is a scheme in which a dataretransmission is made at an arbitrary time.

FIG. 3 illustrates a radio frame structure in a 3GPP (3^(rd) GenerationPartnership Project) LTE (Long Term Evolution). It may refer to 3GPP TS36.211 V8.3.0 (2008-05) ‘Technical Specification Group Radio AccessNetwork; Evolved Universal Terrestrial Radio Access (E-UTRA); Physicalchannels and modulation (Release 8)’.

With reference to FIG. 3, a radio frame may include ten subframes, and asingle subframe may include two slots. A single slot may include aplurality of OFDM symbols in a time domain. A single slot includes sevenOFDM symbols, but the number of OFDM symbols included in the single slotmay vary according to a cyclic prefix (CP) structure.

The structure of the radio frame is merely illustrative, and the numberof subframes included in the radio frame and the number of slotsincluded in the subframes may vary.

Primary synchronization signals (PSSs) (P1 and P2) are positioned at thelast OFDM symbol of the 0-th slot and the 10-th slot. The two PSSs (P1and P2) use the same primary synchronization code (PSC). The PSS (P1 andP2) are used to obtain an OFDM symbol synchronization or slotsynchronization. In the 3GPP LTE, three PSCs are used, and the BSselects one of the three PSCs according to a cell ID and transmits thePSSs (P1 and P2) through the last OFDM symbol of the 0-th slot and the10-th slot.

Secondary synchronization signals (SSSs) (S1 and S2) are positioned atan immediately previous OFDM symbol of the last OFDM symbol of the 0-thslot and the 10-th slot. The SSSs (S1 and S2) and the PSSs (P1 and P2)may be positioned at the contiguous OFDM symbols. The SSSs (S1 and S2)are used to obtain frame synchronization. The SSSs (S1 and S2) usedifferent SSCs (Secondary Synchronization Codes). Namely, the first SSS(S1) uses a first SSC, and the second SSS (S2) uses a second SSC.

A physical broadcast channel (PBCH) is allocated to 0-th to 3-rd OFDMsymbols of the second slot. The PBCH is transmitted in units of 40 ms(namely, in units of four radio frames). The PBCH carries systeminformation the MS requires for its connection with the BS at an earlystage.

In the radio frame structure, the PSSs, the SSSs and the PBCHs aretransmitted through a subframe #0 300 and a subframe #5 350. Thus, thesubframe #0 300 and the subframe #5 350 are those for the MS or the RSto necessarily receive for their connection with the BS.

FIG. 4 illustrates the synchronous HARQ. In the 3GPP LTE, when data isreceived in n-th subframe, the ACK/NACK signal is transmitted in the(n+4)-th subframe.

With reference to FIG. 4, with respect to downlink Data 0 410 receivedin the subframe #0, the MS transmits an ‘ACK/NACK 0’ signal 415 to theBS in the subframe #4.

When the MS receives downlink ‘DATA 1’ 420 in the subframe #1, it maytransmit an ‘ACK/NACK 1’ signal 425 in the subframe #5. In addition,when the BS receives uplink ‘DATA 2’ 430 in the subframe #2, it maytransmit an ‘ACK/NACK 2’ signal 435 in the subframe #6.

It may be difficult to apply such synchronous HARQ to the RS as it is.In general, the RS cannot simultaneously perform data reception from theBS or data relay to the MS in a particular subframe. This is because adata transmission to the MS with respect to a data reception from the BSmay work as interference. This is called a self-interference. Thus, ingeneral, the RS cannot simultaneously perform data transmission andreception in the same frequency band. Likewise, the RS cannot relay datato the BS while it is receiving data from the MS.

Thus, in order to solve this problem, a blank subframe is proposed. Theblank subframe refers to a subframe in which the RS does not transmitdata to the BS or to the MS.

Some or the entirety of subframes may be set as blank subframes.Hereinafter, an entire single subframe is set as a blank subframe, butthis is merely illustrative and the technical idea of the presentinvention can be applicable as it is to a case where only a part of asubframe is set blank which can be interpreted as a partial blanksubframe.

In a case, a certain subframe within a radio frame cannot be designatedas a blank subframe. For example, in the 3GPP LTE system, the PSS andthe SSS are transmitted in the subframe #0 and the subframe #5 in theradio frame. In addition, generally, a paging message or the like isbroadcast in the subframe #4 and/or the subframe #9. The subframes #0,#4, #5, and #9 are those for the MS to necessarily receive for itsconnection with the BS, so in these subframes, the RS cannot be operatedin a data reception state and needs to be operated in a transmissionstate. Thus, the subframes #0, #4, #5, and #9 cannot be defined as blanksubframes. These subframes are called non-blankable subframes. If thereis a non-blankable subframe, how HARQ is to be performed between the RSand the BS and between the RS and the MS matters.

FIG. 5 illustrates performing of synchronous HARQ between the RS and theBS when there is a non-blankable subframe, in which the shaded boxesrepresent the non-blankable subframes in which the RS is in atransmission state.

In FIG. 5, a DL (RS) indicates subframes of the RS at a downlink band, aUL (RS) indicates subframes of the RS at an uplink band, and a UL(Relayed MS) indicates subframes at an uplink band of the MS connectedwith the RS. In FIG. 5, TXs within the subframes indicate that data orthe like is being transmitted in the corresponding subframes, and RXswithin the subframes indicate that data is being received. Namely, inthe subframes of the DL (RS), TXs indicate that the RS is transmittingdata or the like to the MS at a downlink frequency band in the subframesconcerned, and RXs indicate that the RS is receiving data or the likefrom the BS at the downlink frequency band. In the subframes of the UL(RS), TXs indicate that the RS is transmitting data or the like to theBS at an uplink frequency band in the subframes concerned, and RXsindicate that the RS is receiving data or the like from the MS at theuplink frequency band. In the subframes of the UL (Relayed MS), TXsindicate that the MS is transmitting data or the like to the RS at theuplink frequency band.

With reference to FIG. 5, the RS is in the transmission state (TXs) tothe MS in the non-blankable subframes among the subframes belonging tothe DL (RS). Here, the subframes #0, #4, #5, #9 are defined as thenon-blankable subframes, but they are merely illustrative and thelocations and number of the non-blankable subframes are not limited.

The RS receives a scheduling message from the BS in a subframe #1 501 ofthe radio frame #0. The scheduling message includes resource allocationinformation for the RS to transmit data to the BS. The RS transmits dataaccording to the scheduling message in a subframe #5 502 of the radioframe #0. The RS receives an ACK/NACK signal with respect to the datafrom the BS in a subframe #1 503 of the radio frame #1. Here, theACK/NACK signal is assumed to be a NACK signal. Then, the RS transmitsre-transmission data to the BS in a subframe #5 504 of the radio frame#1.

Subsequently, the RS receives a NACK signal with respect to the datafrom the BS in a subframe #1 505 of the radio frame #2. The RS transmitssecond retransmission data to the BS in a subframe #5 506 of the radioframe #2.

The RS receives a NACK signal with respect to the data from the BS in asubframe #1 507 of the radio frame #3. The RS transmits thirdretransmission data to the BS in a subframe #5 508 of the radio frame#3.

The period by which a next data transmission is made after a first datatransmission is an interval of 10 subframes, which is called HARQperiod. Here, in order to prevent reception of an ACK/NACK signal in thenon-blankable subframes, HARQ period is set as the interval of 10subframes. Meanwhile, synchronous HARQ may be performed between the MSand the RS. Here, the synchronous HARQ is performed by the interval of 8subframes of the HARQ period. Namely, it is assumed that the MStransmits initial data to the RS in the subframe #1 520 of the radioframe #0. Then, the MS transmits first retransmission data in a subframe#9 of the radio frame #0, a next HARQ period.

When the HARQ process continues, the MS transmits third retransmissiondata to the RS in a subframe #5 523 of the radio frame #2. In thisrespect, however, because the RS is already transmitting the secondretransmission data to the BS in the subframe 506, the RS cannot receivethe third retransmission data from the MS. This is called a HARQcollision.

When HARQ is performed at the RS, the collision between the HARQ betweenthe BS and the RS and the HARQ between the RS and the MS needs to beconsidered. In addition, the performance of the MS should not beaffected whether or not RS is applied. Similarly HARQ performance of theMS should not be affected regardless of the application of the RS.

FIG. 6 is a flow chart illustrating the process of an HARQ performingmethod according to an exemplary embodiment of the present invention.

With reference to FIG. 6, in step S610, the RS sets an HARQ process withthe BS. The BS may inform the RS about a parameter related to thesetting of the HARQ process through an upper layer message, e.g.,through a radio link control (RRC) message. In this case, the HARQprocess may be set as a synchronous HARQ. The HARQ process may be set inthe form of HARQ period series (to be described).

In step S620, the RS determines whether or not an ACK/NACK signal couldbe received in a corresponding subframe.

With respect to each transmission time point, when the RS can receive anACK/NACK signal at the conventional synchronous ACK time point (afterfour subframes in case of the 3GPP E-UTRA system), the RS receives anACK/NACK and/or a scheduling message with respect to a next transmissionfrom the BS in the corresponding subframe (S630). If reception at theconventional synchronous ACK time point is not possible, the RS receivesthe NACK/NACK and/or the scheduling message from the BS in the firstreception-available subframe after the corresponding time point (S640).Accordingly, if the scheduling message is received at a time point whichhas been delayed compared with the synchronous ACK time point, thecorresponding scheduling message is interpreted to be applied to asynchronous retransmission time point of a previous transmission withrespect to the BS. If the received signal is NACK, the RS performs theoperation again starting from step S615, for a re-transmission, whereasif the received signal is ACK, the HARQ performing is terminated (S650).In the following description, the method of regulating a transmissiontime point according to FIG. 6 is called a<first transmission time pointregulation method>.

FIG. 7 illustrates an HARQ operation according to an exemplaryembodiment of the present invention. DL (RS) indicates subframes of theRS at a downlink band, UL (RS) indicates subframes of the RS at anuplink band. The shaded subframes indicate non-blankable subframes.Subframes marked by TXs represent that data or the like is beingtransmitted in the corresponding subframes, and subframes marked by RXsrepresent that data or the like is being received in the correspondingsubframes. In the following description, subframes #0, #4, #5, and #9are non-blankable subframes.

With reference to FIG. 7, the RS receives a scheduling message from theBS in a subframe #1 710 of the radio frame #0.

The RS transmits data to the BS in a subframe #5 720 of the radio frame#0. If a transmission time point of an ACK/NACK signal with respect tothe data of nth subframe is fixed to come after four subframes (i.e., at(n+4)th subframe), the BS should transmit an ACK/NACK signal in asubframe #9 730 which come after the four subframes of the subframe #5,but at the RS side, the subframe #9 is a non-blankable subframe in whichreception of the ACK/NACK signal is not possible. Thus, the BS transmitsthe corresponding ACK/NACK signal in a subframe #1 740 of the radioframe #1, the nearest subframe available for reception, after thesubframe #9 of the radio frame #0. The reason why the transmission timepoint of the ACK/NACK signal is designated as the nearest subframefollowing the original subframe #9 is that the transmission time pointcomes after the subframe #9 to guarantee a minimum time duration for theBS to decode the data received from the RS and the nearest subframefollowing the subframe #9 is selected as the transmission time point inorder to minimize delay caused by it.

Retransmission data with respect to the ACK/NACK signal is transmittedin a subframe #3 750 of the radio frame #1. Accordingly, the ACK/NACKsignal is received after six subframes from the initial data, and theretransmission data is transmitted after eight subframes from theinitial data. The HARQ period is maintained at the interval of eightsubframes.

The BS transmits an ACK/NACK signal with respect to the retransmissiondata in a subframe #7 760 of the radio frame #1 which comes after foursubframes. The RS transmits second retransmission data in a subframe #1770 of the radio frame #2. Accordingly, the ACK/NACK signal is receivedafter four subframes from the first re-transmission data, and the secondretransmission data is transmitted after eight subframes from the firstretransmission data. The HARQ period is maintained at the interval ofeight subframes. Consequently, by regulating the transmission time pointof the ACK/NACK signals, HARQ can be performed by the HARQ period set asthe interval of eight subframes.

The performing of the above-described HARQ can be represented in theform of series. This is called HARQ period series. In the exampleillustrated in FIG. 7, the HARQ period series may be represented by [(6,2), (4, 4), (5, 3), (4, 4), (4, 4)]. (x, y) represents that an ACK/NACKsignal with respect to n-th subframe is received in (n+x)-th subframeand retransmission data is transmitted in (n+x+y)-th subframe. The HARQperiod is (x+y) subframes. The HARQ periods of the elements belonging tothe HARQ period series are all equal. Thus, the HARQ may be performed ina similar manner to the synchronous HARQ, and compatibility with theexisting synchronous HARQ can be maintained to its maximum level.

Designation of the HARQ period as the interval of eight subframes ismerely illustrative, and there is no limitation in the HARQ period. Inaddition, the number of elements included in the HARQ period series isillustrated to be 5, but the present invention is not meant to belimited thereto.

Meanwhile, in performing HARQ, a minimum time duration for detecting thepresence/absence of a data error and/or a time duration for preparingretransmission data must be guaranteed. For example, it is assumed thatan ACK/NACK signal with respect to data of the nth subframe must betransmitted at least in (n+4)-th subframe or in a subframe after the(n+4)-th subframe. Also, it is assumed that in order to prepareretransmission data with respect to an ACK/NACK signal of m-th subframe,it must be transmitted at least in (m+4)-th subframe or in a subframeafter the (m+4)-th subframe. In this case, if elements of the HARQperiod series are (6, 2), the RS may have insufficient time to prepareretransmission data and fail to transmit retransmission data in thecorresponding subframe. Thus, as a solution, the RS may transmit there-transmission data in a subframe corresponding to a next period. Forexample, with respect to the ACK/NACK signal received in the subframe #1740 of the radio frame #1, it would be preferred for the RS to transmitretransmission data in the subframe #3 750 of the radio frame #1according to the elements (6, 2) with respect to the ACK/NACK signalreceived in the subframe #1 740 of the radio frame #1. However, if timefor preparing the retransmission data is insufficient, the RS maytransmit the re-transmission data at a next transmission time point ofthe corresponding HARQ, namely, in the subframe #1 770 of the radioframe #2. This transmission method can be applicable for a case wherethe BS transmits data to the RS. For example, it is assumed that the BStransmits data to the RS in the subframe #1 740 of the radio frame #1.if the RS cannot transmit an ACK/NACK signal with respect to the data inthe subframe #3 750 of the radio frame #1, the RS may transmit thecorresponding ACK/NACK signal at a next transmission time point of thecorresponding HARQ, namely, in the subframe #1 770 of the radio frame#2.

FIGS. 8 and 9 illustrate other examples of performing of HARQ processaccording to an exemplary embodiment of the present invention. In FIGS.8 and 9, DL (RS) indicates subframes of the RS at the downlink band, andUL (RS) indicates subframes of the RS at the uplink band. Shadedsubframes represent non-blankable subframes. Subframes marked by TXsindicate that data or the like is being transmitted in the correspondingsubframes, and subframes marked by RXs indicate that data is beingreceived in the corresponding subframes. The eight processes in FIGS. 8and 9 show the HARQ operation according to locations of subframes at anearly stage in which initial data is transmitted within the radio framesbased on the embodiment illustrated in FIG. 7.

Table 1 below shows the HARQ period series of each HARQ process in theembodiments in FIGS. 8 and 9.

TABLE 1 Process HARQ period series Process (A) [(6, 2), (4, 4), (5, 3),(4, 4), (4, 4)] Process (B) [(5, 3), (4, 4), (4, 4), (6, 2), (4, 4)]Process (C) [(4, 4), (6, 2), (4, 4), (5, 3), (4, 4)] Process (D) [(4,4), (5, 3), (4, 4), (4, 4), (6, 2)] Process (E) [(4, 4), (4, 4), (6, 2),(4, 4), (5, 3)] Process (F) [(6, 2), (4, 4), (5, 3), (4, 4), (4, 4)]Process (G) [(5, 3), (4, 4), (4, 4), (6, 2), (4, 4)] Process (H) [(4,4), (6, 2), (4, 4), (5, 3), (4, 4)]

As noted from Table 1, the HARQ period series of each process appear asa cyclic shift of the HARQ period series [(6, 2), (4, 4), (5, 3), (4,4), (4, 4)] of the embodiment illustrated in FIG. 7 according to theinitial locations of the subframes.

In the above-described embodiments, the subframes #0, #4, #5, and #9 aredefined as non-blankable subframes, but the locations or the number ofnon-blankable subframes may be altered.

FIG. 10 illustrates performing of HARQ when the subframes #0 and #5 arenon-blankable subframes according to an exemplary embodiment of thepresent invention. DL (RS) indicates subframes of the RS at the downlinkband, and UL (RS) indicates subframes of the RS at the uplink band.Shaded subframes represent non-blankable subframes. Subframes marked byTXs indicate that data or the like is being transmitted in thecorresponding subframes, and subframes marked by RXs indicate that datais being received in the corresponding subframes.

With reference to FIG. 10, first, the RS receives a signal from the BSin a subframe #1 1010 of a radio frame #0, and receives schedulinginformation. The RS transmits a signal to the BS in a subframe #5 1020which comes after four subframes. A synchronous ACK is applied to an ACKwith respect to the transmission signal, so it the ACK is received in asubframe #9 1030 which comes after four subframes. This is, because,unlike the case illustrated in FIG. 7, the subframe #9 1030 can be ablank subframe. In a subframe #6 1040 of a radio frame #2, an ACK withrespect to data before five subframes is transmitted and a schedulingmessage with respect to a transmission after three subframes istransmitted. In the example of FIG. 10, the HARQ period series appear as[(4, 4), (4, 4), (5, 3), (4, 4), (4, 4)]. Compared with the caseillustrated in FIG. 7, the subframes #4 and #9 can be used, so theelement (6,2) of the HARQ period series disappears.

FIGS. 11 and 12 show eight HARQ processes generated according to the<first transmission time regulation method> when the non-blankablesubframes are #0 and #5 like the case illustrated FIG. 10. In FIG. FIGS.11 and 12, DL (RS) indicates subframes of the RS at the downlink band,and UL (RS) indicates subframes of the RS at the uplink band. Shadedsubframes represent non-blankable subframes. Subframes marked by TXsindicate that data or the like is being transmitted in the correspondingsubframes, and subframes marked by RXs indicate that data is beingreceived in the corresponding subframes.

Table 2 below shows the HARQ period series of each HARQ process in theembodiments in FIGS. 11 and 12.

TABLE 2 Process HARQ period series Process (A) [(4, 4), (4, 4), (5, 3),(4, 4), (4, 4)] Process (B) [(5, 3), (4, 4), (4, 4), (4, 4), (4, 4)]Process (C) [(4, 4), (4, 4), (4, 4), (5, 3), (4, 4)] Process (D) [(4,4), (5, 3), (4, 4), (4, 4), (6, 2)] Process (E) [(4, 4), (4, 4), (4, 4),(4, 4), (5, 3)] Process (F) [(4, 4), (4, 4), (5, 3), (4, 4), (4, 4)]Process (G) [(5, 3), (4, 4), (4, 4), (6, 2), (4, 4)] Process (H) [(4,4), (4, 4), (4, 4), (5, 3), (4, 4)]

In Table 2, the HARQ period series of every process appear as a cyclicshift of [(4, 4), (4, 4), (5, 3), (4, 4), (4, 4)] of FIG. 10.

In the example illustrated in FIG. 10, in order to secure a timerequired for channel decoding in the RS also with respect to datatransmitted in the subframe #6 of the radio frame #2 having the element(5,3) of the HARQ period series, like the example of FIG. 7, an ACK/NACKsignal with respect to the corresponding data may not be transmitted ina subframe #9 1050 of the radio frame #2 but be transmitted in asubframe #7 1070 of a radio frame #3.

The processes illustrated in FIGS. 8 and 9 or 11 and 12 may be modified.No matter which HARQ process it is, so long as the sum of the numbers inthe parenthesis of the HARQ period series is 8, the RS can performretransmission of period the interval of 8 subframe. For example, it maybe possible to configure an HARQ process based on the HARQ period seriesof [(6, 2), (5, 3), (5, 3), (4, 4), (4, 4)]. However, because it doesnot follow the <first transmission time regulation method>, an ACK delayof one subframe occurs unnecessarily, so it is ineffective.

The exemplary embodiment of the present invention can be applicable fora case where a single RS has two or more HARQ processes.

FIG. 13 illustrates a method of performing two HARQ processes such thatreception band subframes from the BS do not overlap in the two HARQprocesses. In FIG. 13, DL (RS) indicates subframes of the RS at thedownlink band, and UL (RS) indicates subframes of the RS at the uplinkband. Shaded subframes represent non-blankable subframes. Subframesmarked by TXs indicate that data or the like is being transmitted in thecorresponding subframes, and subframes marked by RXs indicate that datais being received in the corresponding subframes. Specifically, FIG. 13shows, for example, the case where the process (B) of FIG. 8 and theprocess (F) of FIG. 9 are simultaneously performed.

The BS and the RS may simultaneously use two or more HARQ processes eachhaving the mutually overlapping subframes among the HARQ processes asshown in FIGS. 8 and 9 or FIGS. 11 and 12. In this case, receptionsubframes from the BS may be sequentially used one process by oneprocess, for which, a rule may be regulated such that the receptionsubframes do not overlap with each other. In this case, the RS cannotperform reception at the synchronous ACK time point according to the<first transmission time point regulation method>, which includes a casewhere there is a reception subframe from the BS of the previously usedHARQ process. Namely, a subframe which is first available for receptionis determined as an initial subframe which does not correspond to anon-blankable subframe and a subframe used for other HARQ currentlybeing used at the transmission time point. Hereinafter, the transmissiontime point regulation method obtained by modifying the <firsttransmission time point regulation method> will be referred to asa<second transmission time point regulation method>.

FIG. 14 illustrates an example of using two HARQ processes togetheraccording to the <second transmission time point regulation method>. InFIG. 14, DL (RS) indicates subframes of the RS at the downlink band, andUL (RS) indicates subframes of the RS at the uplink band. Shadedsubframes represent non-blankable subframes. Subframes marked by TXsindicate that data or the like is being transmitted in the correspondingsubframes, and subframes marked by RXs indicate that data is beingreceived in the corresponding subframes.

In FIG. 14, the HARQ process (F) of FIG. 9 is first set, and the HARQprocess (G) of FIG. 9 is then set. In the HARQ process (G), thereception subframes are set to be different from those as shown in FIG.9 due to reception subframes used by the first set process. That is, thecase where the elements of the HARQ period series deviate from (4, 4)increases. For example, in case of the radio frame #1, the process (G)is set to be received in a subframe #1 1410 in FIG. 9. In this case,however, because the corresponding subframe has been occupied by thepreviously used process (F), the process (G) is set to be received in asubframe #2 1420 in order to avoid the overlap. In this case, theelement of the HARQ period series is changed from (5, 3) in FIGS. 8 and9 to (6, 2). A similar operation is performed in the subframe #7 1430 ofthe radio frame #2. The BS and the RS may allocate the later set processsuch as the process (G) in FIG. 14 to traffic with a relatively lowlatency requirement or lower priority level.

FIG. 15 illustrates an example of performing HARQ processes when overlapof reception subframes of each HARQ process is permitted. In FIG. 15, DL(RS) indicates subframes of the RS at the downlink band, and UL (RS)indicates subframes of the RS at the uplink band. Shaded subframesrepresent non-blankable subframes. Subframes marked by TXs indicate thatdata or the like is being transmitted in the corresponding subframes,and subframes marked by RXs indicate that data is being received in thecorresponding subframes.

In the case illustrated in FIG. 15, the <first transmission time pointregulation method> is employed as it is, and the resultant HARQprocesses are irrelevant to a set order. When reception subframes of twoor more processes overlap, the corresponding subframes can transfer anACK/NACK signal and/or a scheduling message of all the overlappingprocesses. In case of a subframe #1 1530 of the radio frame #1, thereception subframes of the two processes overlap. An ACK/NACK signalwith respect to the transmission of the respective processes to the BSin the overlapping subframes (i.e., the transmission in a subframe #51510 of the radio frame #0 of the process (F) and the transmission in asubframe #6 1520 of the radio frame #0 of the process (G)) and/or ascheduling message with respect to the next transmission of therespective processes to the BS (i.e., the transmission in a subframe #31540 of the radio frame #1 of the process (F) and the transmission in asubframe #4 1550 of the radio frame #1 of the process (G)). As a result,it features that ACKs with respect to transmissions from the RS to theBS made at two different transmission time points may be transmitted atthe same time point, or scheduling messages with respect totransmissions to the BS at two different transmission time points may betransmitted at the same time point.

As for a transmission time point of an ACK with respect to data receivedby the RS, if two or more HARQ processes are used, the RS may transmitthe ACK by using a transmission time point of another process. Forexample, in the case illustrated in FIG. 13, if the RS cannot transmitan ACK/NACK signal with respect to the data, which have been received ina subframe #1 1310 of the radio frame #1, in a subframe #3 1320 of theradio frame #1, namely, a transmission time point following thecorresponding process, the RS may transmit a subframe #1 1340 of theradio frame #2, namely, the next transmission time point of the sameHARQ process as mentioned above. Alternatively, the RS may transmit theACK/NACK signal in a subframe #7 1330 of the radio frame #1, namely, thenearest transmission time point among the transmission time pointsincluding those of the other process. In this case, informationregarding to which process the ACK belongs is required in the ACKinformation.

The RS sets the HARQ process according to one of those methods asdescribed above or any of their combinations for its communication withthe BS. The BS may inform the RS about a parameter related to thesetting of the HARQ process through an upper layer message, for example,through an RRC message. For example, the RS may perform communicationwith the BS by using one or more HARQ processes semi-statically. In thiscase, the BS may change the amount, location, modulation scheme, and acoding scheme of resources used by the RS at each subframe through ascheduling message. The RS may allocate an HARQ process which is notused for its communication with the BS to the MS connected thereto tothereby perform communication with the MS without a collision. Inaddition, the RS and the BS may fix the amount and location of the radioresources within the semi-statically used HARQ(s) like semi-persistentscheduling. In this case, the BS does not transmit schedulinginformation with respect to the RS at every subframe, but transmits onlyACK/NACK with respect to data the RS has transmitted, and data. In thiscase, the BS transmits a corresponding message only when the type of asemi-statically allocated HARQ process or the amount and location ofradio resources within a particular HARQ process change.

FIG. 16 is a schematic block diagram of an RS according to an exemplaryembodiment of the present invention. The RS 1600 includes a transceiver1610 and a processor 1620. The transceiver 1610 receives data from a BS(or an MS) and relays the data to the MS (or the BS). The processor 1620is connected with the transceiver 1610 and serves to process the datareceived from the transceiver 1610 and relay it. The HARQ performing asshown in FIGS. 6 to 19 may be implemented by the processor 1620.

The methods as described above can be implemented by processors such asa micro-processor, a controller a microcontroller, an applicationspecific integrated circuit (ASIC), and the like, according to softwarecoded to perform the methods or program codes. It will be understoodthat designing, developing, and implementing the codes may be obvious tothe skilled person in the art based on the description of the presentinvention.

The preferred embodiments of the present invention have been describedwith reference to the accompanying drawings, and it will be apparent tothose skilled in the art that various modifications and variations canbe made in the present invention without departing from the scope of theinvention. Thus, it is intended that any future modifications of theembodiments of the present invention will come within the scope of theappended claims and their equivalents.

What is claimed is:
 1. A method for performing a hybrid automatic repeatrequest (HARQ) in a wireless communication system, the methodcomprising: determining, by a relay station (RS), a plurality ofallocated downlink (DL) subframes which are used by the RS to receivescheduling information from the BS; determining, by the RS, a pluralityof uplink (UL) subframes for performing a HARQ with the plurality ofallocated DL subframes, each of the plurality of UL subframescorresponding to each of the plurality of allocated DL subframes,assigning, by the RS, sequentially each of a plurality of HARQ processesto each of the plurality of UL subframes one by one; and performing, bythe RS, HARQ with the BS at least one of the plurality of HARQ processesassigned to the plurality of UL subframes, wherein a n-th subframe isconfigured for a corresponding UL subframe if (n−4)-th subframe isconfigured for one of the plurality of allocated DL subframes, where ndenotes an integer, wherein the plurality of allocated DL subframes areconfigured in at least one radio frame having 10 subframes indexed from0 to 9, and wherein subframes of the 10 subframes having indexes 0, 4, 5and 9 are not configured as an allocated DL subframe.
 2. The method ofclaim 1, further comprising: receiving information on a number of theplurality of HARQ processes from the BS.
 3. The method of claim 2,wherein the number of the plurality of HARQ processes is not greaterthan eight.
 4. A relay station (RS) configured for performing a hybridautomatic repeat request (HARQ) in a wireless communication system, theRS comprising: a transceiver configured to transmit or receive a radiosignal; and a processor operatively coupled with the transceiver andconfigured to: determine a plurality of allocated downlink (DL)subframes which are used by the RS to receive scheduling informationfrom the BS; determine, based on the received information, a pluralityof uplink (UL) subframes for performing a HARQ with the plurality ofallocated DL subframes, each of the plurality of UL subframescorresponding to each of the plurality of allocated DL subframes, assignsequentially each of a plurality of HARQ processes to each of theplurality of UL subframes one by one; and perform HARQ with the BS atleast one of the plurality of HARQ processes assigned to the pluralityof UL subframes, wherein a n-th subframe is configured for acorresponding UL subframe if (n−4)-th subframe is configured for one ofthe plurality of allocated DL subframes, where n denotes an integer,wherein the plurality of allocated DL subframes are configured in atleast one radio frame having 10 subframes indexed from 0 to 9, andwherein subframes of the 10 subframes having indexes 0, 4, 5 and 9 arenot configured as an allocated DL subframe.
 5. The RS of claim 4,wherein the processor is configured to receive information on the numberof the plurality of HARQ processes from the BS.
 6. The RS of claim 5,wherein the number of the plurality of HARQ processes is not greaterthan eight.